ml taylor



ug 9 27 A. M. TAYLOR ELECTRIC POWER TRANSMISSION SYSTEM Filed VJam. ll. 1927 Cal Patented Aug. 9, 1927.

unirse STATES PATENT orifice.

Atrium MILLS Tarma, on nRDrNGToN, BIRMINGHAM, ENGLAND.

ELECTRIC POWER-TRANSMISSION SYSTEM.

Appucation fui-af January 117 1927, sei-iai Nef; 160,494jana in eri-:a1: Britain Juiy 1r', 1925.

The present invention is an improvement in` or modilication of, the invention claimed in my British Patent No. 232,275, more particularly oit that part relatingi to a. combined overhead and underground transmission.

The particular feature introduced in my British Patent No. 232,275 was the transmissien'of the charging current (or capacitance current) required' for the intermediate and outermost insulations through the central core'of the cablev (or, where overhead tlirougjh a single overhead. wire'per phase, connected directly or indirectly, with the central core ot the cable)I ata higher voltage than it would? otherwise be transmitted at, andthe reduction thereby of the volume of the capacitance current'A required to be transmitted ,through the overhead line-or, wherethe lineis exclusively an undergroundr cable, through the intermediate and outermost cores ot that cable.

. The pi cient invention still? retains the feature ot the transmission of the capacitance current at the highest possible voltage and its redistribution at the receiving end at reduced' voltages; but its purpose is, while still retainingA the above feature, tostill further reduce the capacitance current; and

ralso incidentally 'theload current-by transmitting the same at a voltage considerably above that which even. the bestv designed cable ltnown to the art would be capable of sustaining. Tt takes account of the fact that, while the underzgrround4 cable cannot be constructed, under present known methods, for a Wiltagel ot operation` appreciably above 90,000A`r volts above earth (150,000 betweenphases) an overhead line can be constructed having a yvoltage of 127,000 v. above earth (220,000 between phases); and it seeks to discover means whereby, without transformingr the whole of the' power to be transmittcd (andi thereby incurring rather serious loss inf operation` as well as a quite'unnecessary capital outlay), the advantages ot the aforesaid lgreat increase inA the voltage',V in

the way of reduction of the capacit-ance current' required tobe transmitted for charging' the ends of the line, where the latter goes underground, as wellas the great reduction inthe amountv` of the power component-ofrv the current whichv` has `toI be transmitted through the overhead: line, canbe realized. ln particular,- the application of the e tl tupment of' a railway vline vregular railway loads, be very'large commercial loads dealing with thel whole supply of power to the towns through which the line passes. TheseT loads will have a power factor under present circumstances of between 75% and 85% and` at this power factor there is a very large lagging wattless ycomponent' inthe current, which represented? electromagnetic stored energy. This stored energy ten'ds to supply the cable charging current corresponding to'. a certain section of the line. II the towns at which this stored energy was available were all of equal? sizer and situated at uniform distances apart, the problem of the supply of the requisite charging currents for the caliles would beA an easy one-assuming, that is, that the underground cable would be required along the whole length of' the line into which it was desired to feed the requisite capacityA current.l p

Unfortunately, however, this is not the case; there are very large centres of populationf followed by' veryf large `traps wherethere is no population, and' the present inventor has satisfied' himself, by a detailed calculation of such a line, that the distances to which it isi required to feed the electro-magnetic` stored energy (expressed as charging` current)` would be so great that, onty the system proposed in his British Patent No. 232,275, this could not be done, even it a special overhead line were run Jfrom any such centre both ways for, say, 50 miles or so, ywithout some auxiliary means. Such auxiliary means might consist of an induc- '7 tance inserted? at the substation (at the town under consideration) between g the bus-bar and each of the branches of the overhead line.V Such an arrangement would boost up the voltagel of the charging current at the said-"substation, .andl the pressure in the overhead line which transmitted this charging current backwards towards the main `,feneratin'ggg station and forwards awayy from it. would 'gradually fall until, at the point where it joined up with the underground cable system, it would be'at the same potential; as, Yfor example, the potential' of the innermost core ot the cablev system to which it was Yjoined. (gt is here assumed, for the mein nt, that' t 1e nple-concentric ,cables in' the present invente-Pls British ductances by a primary winding of a. transformer, or by an auto transformer, we may at once increase the voltage of the overhead line to, say, 220,00() volts and thereby very greatly reduce both capacitance current and the load current, and by this very factthe potential drops which occured in the pas- Y sage backwards and forwards of the capaci tance current, to the pointsfwhere the latter was to be fed into the line, are now `very greatly reduced, and in additio we areable to put a .large portion of the oad current into the overhead line at the high pressure.

The'overhead line is. moreover, by virtue of the fact that the winding of the trans` former is in a branch circuit to the over` head lineavailable for ythe passage both of through load current and of capaci- L'tance current for the towns beyond, without either of these currents having to traverse any unnecessary lnductance, the importance of which on starting up thecline, after a stoppage, may be considerable. By the said arrangement, therefore, we have provided a means whereby each` individual large town is able to contribute a lagging component of current suflcient to charge the cable system to great distances from its origin, and in this manner during the ordinary working-of the system the transmission of capacitance current from thc generating station to the extreme end of tb#` line, perhaps one or two hundredmiles away, is avoided. Secondly, the assistance of the overhead line for the transmission. at considerably increased voltage, of the load current is secured; and thirdly the heating of the underground'cable, consequent upon the necessary transmission of large charging `currents over long distances from the various sub-stations (at the lower voltage) is avoided, and the cable isnonsequently left free for the passage of larger load currents. Lastly, the advantage of the combination ofthe undergroundand overhead system is secured, the underground svstem being less likely to interruption than the overhead system and acting as a standbyv to the latter in the event, for example. of its being struck by lightning or by an aeroplane.

The advantages of the utilization of the lagging component of theload at the substations, for the purpose of charging the under ound cable would not, however, be availa le, if there were any risk in so working of current resonance? coming in and passing currents which were never intended bet-Ween the'inductance in the consumers motors and the capacitance in the underground cable. The inventor gets over this as follows It is arranged that, at the time of maximum load at a sub-station, such a length of cable on either side of the sub-station will be fed from that substation as will approximately require 'a current equal to, or somewhat less than, the lagging component of the load current. f

lVhen this is so arranged. it follows that every consumer whose load is taken off the system, also thereby removes the equivalent of a parallel reactance from the general sub-station system. The resultant reactance of the sub-station system is thereby increased. Hence it follows that the natural period of oscillation for the whole transmission system falls (and cannot possibly rise). If, for example, the normal periodicity of the system is say cycles per second and if, at this periodicity the amount of lagging load current is properly 1 arranged for, then when, for instance. the load current is `quartered by the switching on' of consumers loads, (assuming the said load current to be all a motor current) the equivalent reactance ofthe load circuit is increased fourfold and, since the natural period of resonance depends upon the square root of the reciprocal of the inductance. it follows that the new natural period of resonance becomes one-half--L e. a half a. cycle will cover two half cycles of the fundamental. But half the frequency of oscillation, applied to the cable system, will only pass half the charging current; consequently, instead of there being any tendency to current resonance, the reverse is the case as the load of the sub-station goes off; and therefore the condition is one of perfect safety.

It should be explained that where the overhead line feeds the capacitance current back into the underground cable as for example at a mid point between two substations, or any other suitable points. a substation will have to be produced for the purpose of housing the (small)k transformer which transforms down the pressure of the capacitance current to that suitable for the core or cores of-the underground cable or cables; but, as indicated, the transformer for this purpose need `be only quite small, and there need be no automaticl switch gear unless considered desirable.

The arrangement described above would apply'to a long distance railway transmission where, in order to save unnecessary capital outlay a portion of the load current fissati? is arranged 't6 be ieri-'barras @verite-rianne directly yfrom they generating station, in conjunction with a substation, for subst'ations, which feed tliec'apa'city 'current `baclmfards and forwards over their own sections 'of the line. In the case, however, of an extremely important railway service, it would benece'ssary t'o ensure that a possibleinterruption "of the supply on the overhead 'system will not put the line out of commission, and hence it is desirable that all the load current` should be supplied through the underground cable system, leaving only the Capacitance current'to be dealt with by the overhead line.

A breakage in the overlrieady line would,`in this case, only afec-t the supply of capacitance current to a comparatively shoi't's'ec- Lil) tion of the underground cable andthe said section could receive its supply partly from a load substation and artly from a dummy substatiol'i without a serious menace to the heating of the saidI underground cable. e

In the case of a long transmission line that is not laid along the railways, as forexai'nple where Waiter power isb'eing' transmitted over aver'y'long line which terminates for vexample at thecentre of a large town, it is desirableto terminate the overhead line at "the outskirts of the 'aforesaid town and link up with a' main 'substation at the lcentre' of the said town andtodo this bvrn'eans ot undergroundcables, which, in this casev may or may not be carried lbackwards towards the generating station, beyond theat the outskirts of the town and to feed it into the outermost and intermediate insulations of' the underground cable;

Also, in order to utilizeas far as possible" the current-carrying capacity of all the three cores oi the triple concentric cable"(if such be used) for the passage of load current and capacitance current. to the centre ofl the town, itis desirable, at the outskirts of the town, to erect a house *containing a small transformer and to insert between the overhead line and the innermost core ofthe un# derground cable the primary coil of a transformer, whose 4 two or ymore secondaries can teedhoth load current and capacitance current, in such proportions as may be desired, along the outermost, intermediate and innermost `cores of' the' underground cable to the mainsubstation, vwhere again thecapalci- Y `tance current may be partly reedistributed as found convenient. 'The distribution of the capacitance current among the ditl'erent 'cores may be facilitated by the employment or inductances inserted between the transformersandf the cores, at both ends of the underground cable, in the manner indicated in rmy rti'shPatent No. 232,275.

Referring now to the drawings, Fig. l gives a generalview of the electric circuits at a big substation, corresponding with a large town, and including the underground cable 'and the overhead line in both directions from the said town towards other towns at considerable distances away, suoli as along a line of railway. It" also shews the two feeding points 'of the overhead line into the underground cable system at the siiafll transformer houses alluded to in the specification.

It also shews the way in' which the eX- treinely high voltage of the overhead line is transformed down to the pressure existing 'in the underground v4cable and the way in which the capacitance current and the load current taken' from the overhead lineare converted and sub-divided and fed into the different cores of the underground cable.

Fig. 2 represents 'the end of an overhead `transmission as it arrives at the outskirts or a large town. It represents the electric circuits from this point onwards into a main transformer 'stationin tli'ecentre of the town which is connected with the small transrformery station at the outskirtsof the town by means of underground cables. It also shews h'ow the high pressure current taken from the overhead line (which operates at extremely high pressure) is transformed d'oivn and fed into thevarious cores oi the underground cable for the purpose of transmission to the main transformer'station in the centre of the town.

o Referring now in detail to Figure 1 (O.

L.) represents the overhead line, (E)'rep resents a longitudinal section ythrough the surface ofthe groundparallel with the overhead line, represents the lead sheathingbf the cable. Y A1, A2', A3, represent respectively the innermost. thev intermediate and the outermost cores of a triple concentric cable (of which L. S. represents the lead shea-th. At the principal sub-station (the centre'onev in the' diagram), representing a big town. (P) represents the primary winding of the main transformer and the lou7 tension secondary winding of same (C. M.) represents the motor load ofi the town, consistintr of consumers motors (C.

This motor load has a 'large lagging component of current which, passing through the secondary winding sets up a lagging current in the primary winding (P) which` being fed into the overhead line (O. L.) is

vtaken into the primary winding. (P) of the small transformer, at the halt-way transformer house shew-n at the leftof the figure,

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and is there fed as a leading current. into the underground cable', beingk distributed among the different cores of the said underground cable by means of the two secondary coils Si, S2.

Coming back to the main transformer at the princi al substation, the three secondary coils S1, IS? and, if desired S3, distribute any capacity current which may be sent from the main generating station along the overhead line (for purposes of charging up the overhead line) suitably amongthe three cores of the underground cable. v The sub-station shown onv the ri ht hand Side ofthe figure is precisely simi ar in all respects to that shewn on the left hand side and fulfils similar functionsi. e. the lag- 'ging component of the current received from ing the right hand section of the underground cable system by means of the extension of the overhead line (O. L.) as shewn. v

VMoreover, as already indicated earlier in thisl specification, a through current (whether a load current ora capacitance current) can be passed right through ,the aforesaid main` substation 4to other distant .sub-` stations situated in similar large towns and also, it atv any time the line has to be charged up after an interruption, the capacity current can be sent `from themain generating station by means of the overhead line to any of the principal substat-ions desired.

Referring now in detail to Figure 2 (O.

L.) is the overhead line, (E) is the longitu-4 and, if desired-Ss are secondary windings employed to 'transform and distribute both capacitance currentand load current'1 into the Vcores A1, A2 A, of the underground cable. yL. S. is the lead sheathing of thel said cable.y (L) and (L) are inductances which maybe inserted if desired between the transformer and the cores of thecable for the purpose of boosting up the capacity current. i

At the centre of the town the main transformer station (M. T.) is equipped with ay primary winding (P) divided into three sections and connected with the cores A1 A2 As of the underground cable; S is the sec-y ondary winding andC. M. is the consumers motor load, the lagging component of which underground cable, the current will be passed from the small substation to the big substation through the central core of the cable at ahigher pressure and b means of the transformer at the main su station, it

vwill be transformed and fed back at lower pressure into the yright hand end of the rconductor As in the manner indicated. If the consumers motors is employed for feeddesired, this may be repeated in connection with the conductor A2.

In all the above diagrams and description, it will be noted that only that part of the circuit is illustrated and described which corresponds to a sin le-phase with the neutral pointrearthed. y e diagram may therefore apply either to a three-phase system (in which case two other precisely similar phases would be added, each having the neutral point earthed) or they may apply to a-two-phase system, or a four-phase system, in which either two circuits at right angles to one another, or four circuits each 900 apart (in each case having a common neutral conductor) would be employed.

Having now particularly described and ascertained the nature of my said invention and in whatmanner the same is to be performed, I declare that what I claim is 1. In a high-tension alternating-current transmission system, transmission conductors including the combination of overhead lines and intersheathed underground cables, means to transmit current through said overhead lines and underground cables at a high. voltages on the inter-sheathed cables and a relatively higher voltage on the overhead lines than thelimits possible with the `underground cables, and transformers with tappings connecting the overhead lines and cores of the cables for distributing the potentials and adjusting the Vloads on the individual cores of the cables.

2. In the arrangement of the transmission vsystem claimed in claim 1,'a parallel arrangement of conductors including a conytinuous underground cable and a parallel overhead line, in which `the cable and overheadline act as standbys for each other.

. 3. In. a high-tension alternating-current transmission system, transmission conductors including'V the combination of overhead `linesand intersheathed underground cables at intervals along said overhead lines, means to 'transmit current throu h said overhead l linesandunderground cab es at high voltlosv ages on the intersheathed cables and a relatively higher voltage on the overhead lines than the limits possible with the underground cables, and auto-transformers with tappings connecting the overhead lines and cores of the cables at the ends and mid points thereof for distributing the potentials and adjusting the loads on Athe individual cores oit the cables, whereby the distance ot' transmission may be increasedy and the length ot the underground cable may be reduc-ed.

4. In a high-tension alternating-current transmission system, transmission conductors including the combination of overhead lines and intersheathed underground cables7 means to transmit current through said overhead lines and underground cables at high voltages on the intersheathed cables and a relatively higher voltage on'the overhead lines than the limits possible With the underground cables, transformers with tappings connecting the overhead lines and cores of the cables for distributingA the potentials and adjusting the loads on the individualy cores of the cables, and means to supply lagging currents to said Conductors, including, in addition to lagging currents taken from consumers loads, compensating reaotances for adjustment oi said laggin@f D currents.

5. In a high-tension alternating-current transmission system, transmission conductors including the combination of overhead line and intersheathed underground cables at ends and inte 1vals along said line, means to transmit current through saidV overhead line and intersheathed underground cables at a higher voltage on the overhead line than n the intersheathed underground cables, means to supply lagging currents to said .conductors including lagging currents taken from Consumers loads at said ends and intervals along theline and compensating reacta-nces for adjustment of said lagging currents, auto-transformers with tappings and reactances for the triple purpose of connecting ends and midpoints of said intersheathed cables With-said overhead line, for adjusting leads on individual cores and distributing potentials on said cores, with the object ot increasing the distance of transmission and reducing the length and voltage of the underground cable. f

In testimony whereof he aiixes his signature.

Dated this 5th day of May, '1926.

' ALFRED MILLS TAYLOR. 

